Surface acoustic wave sensors

Abstract

Pressure sensing diaphragms comprise a cylindrical or spherical crystalline member in which an internal cylindrical or spherical chamber is provided. In the internally loaded embodiments, a fluid is introduced into the chamber and the pressure exerted by the fluid causes generally tensile stress in the region of the diaphragm generally about the chamber. In the externally loaded embodiments, the diaphragm is immersed within the fluid and the pressure exerted by the fluid causes generally compressive stress in the region of the diaphragm generally about the chamber. For each of the embodiments, the stresses arising cause certain mechanical and electrical properties of the crystalline material to change. The change in these properties is detected by observing the frequency behavior of one or more oscillators whose frequencies of operation are controlled by respective surface acoustic wave devices provided in the regions of elastic deformation. Many diaphragm arrangements are capable of providing temperature compensated pressure measurements. Two particularly useful orientations for the temperature compensated embodiments are the SST and ST orientations.

What is claimed is: 
     
       1. A surface acoustic wave signal frequency apparatus comprising a crystalline diaphragm section having a cylindrical or spherical outer surface and a cylindrical or spherical inner surface, said outer surface being adapted for subjection to an applied isotropic force and said inner surface having an area thereof of a selected crystal lattice arrangement and adapted for the fabrication of a surface acoustic wave device. 
     
     
       2. A signal frequency apparatus as in claim 1 wherein said diaphragm section has a continuous crystal lattice structure.